This invention relates generally to chillers, and more particularly, but not exclusively, provides a system and method for increasing the efficiency of chillers.
Absorption chillers provide chilled water for use in a range of industries including the plastics industry; the printing industry; the magnetic resonance imaging (MRI) industry; the heating, ventilating, and air conditioning (HVAC) industry; and the laser cutting industry. In HVAC applications, absorption chillers pump chilled water to air handling units (AHUs) in buildings, such as warehouses and high-rise buildings. The AHUs for each section of the building open and close to let the chilled water flow through so as to keep the section at a desired temperature.
FIG. 1 is a block diagram illustrating a conventional single stage absorption chiller 100. The chiller 100 includes a generator 105; a separator 110; a condenser 120; an expansion valve 130; an evaporator 140; an absorber 150; and a heat exchanger 160, each coupled in series, respectively. The chiller 100 enables the chilling of water via absorbing and then releasing water vapor into and out of a lithium bromide (LiBr) solution. A heat source, such as a natural gas burner, applies heat to the generator 105, which contains LiBr and a refrigerant, such as water, in liquid form. The LiBr and refrigerant phase change to a vapor state and are then separated in the separator 110. The LiBr is transferred to the absorber 150 via the heat exchanger 160, in which the LiBr is phase changed back to liquid form.
The refrigerant, in vapor form, is transferred to the condenser 120, within which cooling water circulates in pipes. The cooling water can be supplied from a utility company, water tower, or other water source. The condenser 120, using the cooling water, cools the refrigerant vapor and transfers it to the evaporator 140 via the expansion valve 130. The expansion valve 130 reduces the pressure of the refrigerant vapor.
The evaporator 140 then transfers ambient heat from the chilled water received from an application (e.g., AHUs) to the water vapor. Accordingly, the chilled water is then cooled and returned to the application. For example, the chilled water may enter the evaporator 140 at 54xc2x0 Fahrenheit and may leave the evaporator 140 at 44xc2x0 Fahrenheit.
The refrigerant then leaves the evaporator 140 and recombines with the LiBr in the absorber 150, within which cooling water circulates, which causes the refrigerant to change state back to a liquid form. The LiBr and refrigerant are then transferred to the generator 105 (via the heat exchanger 160) to repeat the above-mentioned process.
Conventional chillers, such as chiller 100, are very efficient compared to other mechanisms used to cool buildings. In addition, conventional chillers use water as a refrigerant, instead of environmentally damaging chloro-fluoro-carbons (CFCs). However, conventional chillers do exhibit some inefficiencies. For example, chilled water and cooling water are generally pumped into and out of conventional chillers at fixed rates, regardless of the load. The same amount of electricity might be used to pump chilled water and cooling water on a cool day as on a hot day. Further, valves located between the pumps and the chiller limit the inflow of water, thereby wasting energy on pumping.
As shown in FIG. 2., one technique of overcoming the above-mentioned deficiency is to install a transducer feedback mechanism that controls the pumps. FIG. 2 is a block diagram illustrating a chiller system 200 that includes a transducer feedback mechanism. The chiller system 200 includes a chiller, e.g., chiller 100; a pump 210; a variable frequency drive (VFD) 220; a valve 205; a transducer 260; AHUs 230, 240, and 250; and corresponding valves 270, 280 and 290. The pump 210 is controlled by the VFD 220, which receives load feedback from transducer 260. The pump 210 is in fluid communication with chiller 100 via the valve 205 and the AHUs 230, 240 and 250. The valve 205 limits water flow into the chiller 100 so as to prevent pipe erosion.
During operation of the chiller system 200, pump 210 pumps chilled water into chiller 100 to the valves 270, 280 and 290. If valve 270 is open, then chilled water will flow to AHU 230. Similarly, if valve 280 is open, then chilled water will flow to AHU 240. If valve 290 is open, chilled water will flow to AHU 250. After the chilled water flows through the AHUs 230-250 (if their respective valves are open), the chilled water returns to the chiller 100. If all the valves 270, 280 and 290 are closed, then no chilled water will flow to the AHUs 230, 240 and 250 and the chilled water will return to the chiller 100 via a bypass 255.
The transducer 260 measures the differential pressure at points A and B. The transducer 260 then transmits a signal proportional to the differential pressure to the VFD 220 via a relay 225 to either increase or decrease the rate that pump 210 pumps chilled water. However, the differential pressure measured by the transducer 260 is not necessarily related to the load. For example, if all the valves 270, 280 and 290 are closed, the transducer 260 may measure a differential pressure not indicative of the actual load. Accordingly, the transducer 260 may cause the VFD 220 to drive the pump 210 at greater speeds than required, thereby wasting electricity. In addition, the transducer 260 is susceptible to dirt (causing erratic control of the chiller 100) and often fails.
Accordingly, a new absorption chiller system and method is required that solves the above-mentioned deficiency.
The present invention provides a system for increasing the efficiency of a chiller. The system comprises a chiller, a burner, a first variable frequency driver and pump, a second frequency drive and pump, and a feedback system measuring burner characteristics. The chiller has a chilled water input and a cooling water input and the burner is coupled to the chiller. The first variable frequency drive and pump is coupled to the chilled water input. The second variable frequency drive and pump is coupled to the cooling water input. The feedback system is coupled to the burner, the first variable frequency drive, and the second variable frequency drive. The feedback system is capable of measuring a characteristic of the burner that is proportional to the cooling load of the chiller system and then transmitting a signal corresponding determined characteristic to the first and second variable frequency drives.
In an embodiment of the invention, the feedback system includes a potentiometer that is capable of determining a position of a modulating motor of the burner.
In another embodiment of the invention, the feedback system includes a potentiometer that is capable of determining a position of an energy input valve of the burner.
The present invention further provides a method for improving the efficiency of a chiller system. The method comprises: determining a characteristic corresponding to a cooling load of a chiller; and transmitting, to a variable frequency drive, a signal corresponding to the characteristic, wherein the variable frequency drive is coupled to a chilled water pump. In another embodiment of the invention, the method further comprises transmitting, to a second variable frequency drive, a signal corresponding to the characteristic, the second variable frequency drive coupled to a cooling water pump.
Therefore, the system and method may advantageously increase the efficiency of a chiller system.